Define 'CharacteristicSource' in NRML

[Damiano Monelli]

A new source typology, named 'CharacteristicSource' has to be defined in NRML.

A 'CharacteristicSource' is defined by the following parameters:

- source_id
- name
- tectonic_region_type
- magnitude frequency distribution
- rake
- surface

surface can be one of three typologies:

- simple fault surface (https://github.com/gem/oq-nrmllib/blob/master/openquake/nrmllib/schema/hazard/general.xsd#L100)
- complex fault surface (https://github.com/gem/oq-nrmllib/blob/master/openquake/nrmllib/schema/hazard/general.xsd#L109)
- collection of planar surfaces, where each planar surface is described by:

- strike
- dip
- surface corners coordinates - longitude, latitude, depth: (top left, top right, bottom right, bottom left)

[Lars Butler (lars-butler)]

We'll need to update parser code to support this new type as well.

[Lars Butler (lars-butler)]

Pull request: https://github.com/gem/oq-nrmllib/pull/78

[Lars Butler (lars-butler)]

https://github.com/gem/oq-nrmllib/pull/84